Patent Application
20140017980
A number of gas turbine engines are known and would be familiar to one of skill in the art. Three common types of jet aircraft gas turbine engines are the turboprop, the turbojet and the turbofan, although more exotic and application-specific embodiments also exist. Each engine achieves the desired end result of generating thrust that may be used to propel an aircraft, albeit in a somewhat different manner.
All gas turbine engines generally include a forward intake section for capturing and feeding air to the engine. The intake section is typically followed by a compression section where the incoming air is compressed by a rotating compressor and accelerated. The compressed air is then passed into a combustion section, where heat is added through the burning of fuel to produce a high-velocity gas stream that is passed to a turbine section. In the turbine section, the high-velocity gas stream rotates a turbine, which is connected to and rotates at least the compressor.
In a turboprop engine, the turbine portion of the gas turbine engine is connected by a shaft to the compressor and to a propeller that (typically) resides forward of and outside of the turbine engine housing. Rotation of the turbine thus causes a corresponding rotation of the propeller, which displaces the surrounding air and produces thrust. In a turbojet engine, the turbine is still connected to the compressor, but all of the thrust is typically generated by passing the high-velocity gas stream through a propelling nozzle at it exits the engine. The nozzle constricts the flow of the exiting gas stream, thereby maximizing the velocity thereof.
Of particular interest in the present application is the turbofan engine. Like the turboprop and turbojet engine, a turbofan engine also includes a forward air intake, followed by a compressor section, a combustion section, a turbine section and an exhaust section. In a turbofan engine, however, a rotating fan of typically large diameter resides upstream of the compressor section and within the engine housing, which may also be referred to as a nacelle, case, or duct (hence the “ducted fan” nomenclature often associated with turbofan engines). The fan is driven by the turbine along with the compressor. The fan is used to increase the amount of air that is passed through the engine, thereby increasing the thrust produced by the engine.
Turbofan engines normally come in two variations—low bypass engines and high bypass engines. These designations refer to the ratio of the amount of air that passes through the combustion portion of the engine to the amount of air that passes around the combustion section (i.e., through only the fan). In either case, the fan is typically designed to move as much air as possible through the engine, so the tips of the fan blades normally rotate in very close proximity to the inside of the fan housing. The resultant minimized gap between the fan blades and the interior of the fan housing can be problematic, as gravity, dynamic forces of rotation or flight movement, and/or different rates of thermal expansion, may result in contact between the tips of the rotating fan blades and the interior of the fan housing. This contact typically occurs, but is not restricted to, approximately the 5:00 and 7:00 positions within the fan housing (i.e., along a bottom portion of fan rotation). At a minimum, such contact may damage or cause a wearing of the fan blade tips. If blade-tip-to-housing contact is sufficiently severe, however, engine damage or engine failure may result.
Turbofan engine designers are aware of and usually anticipate the possibility of contact between the fan blade tips and the interior of the engine housing. To this end, the housing interior surrounding the fan is commonly covered with an abradable material, such as in the form of a circumferential contact strip. The abradable material is sacrificial in nature, meaning that it is designed to wear away upon contact with the tips of the fan blades. A number of useable abradable materials would be familiar to one of skill in the art.
When contact between the fan blade tips and the abradable material of the fan housing is detected, it may be desirable to slightly increase the blade tip-to-abradable material minimized gap in the area of contact. The amount of material removed is normally very small—on the order of thousandths of an inch, for example. This makes it very difficult, if not impossible, to acceptably effectuate the removal of abradable material with a power tool. It is also desirable that the abradable material be removed in a manner that follows the contour/curvature of the fan housing and associated abradable material layer. Consequently, it is also very difficult, if not impossible, to consistently effectuate the removal of abradable material by hand—such as by means of a hand-held sandpaper sheet or the like.
It can be understood from the foregoing comments that there is a need for a device and method of efficiently, accurately and consistently removing small amounts of abradable material from the interior of a gas turbine engine housing. Devices and methods of the invention satisfy this need.
The invention is directed to devices and methods by which small amounts of gas turbine engine housing abradable material may be removed along the path of a rotatable engine fan. A device of the invention is generally comprised of an abradable material removal tool having an abradable material contacting base with a handle or other gripping portion extending therefrom. The base is preferably formed from a substantially rigid material with a curved profile that matches the curvature (i.e., circumference) of the abradable material contact surface. A rigid or semi-rigid rib may extend from a top surface or other portion of the base. The rib preferably extends substantially perpendicularly upward therefrom to facilitate handling and use of the tool (i.e., to act as a handle), and may also help to maintain the desired curvature of the base.
An abrasive material, such as a sheet of sand paper, may be affixed to the contacting surface 85 of the base—with the abrasive material facing outward therefrom. The fixed curvature of the base allows the curvature of the abradable material to be substantially maintained when the tool is used in an abradable material removal operation.
The base 55 is also dimensioned and provided with a shape that permits its insertion between adjacent leading and trailing fan blades 20 of the turbofan engine 5. Consequently, a hand-generated back-and-forth rotation of the fan 15 while the abradable material removal tool is positioned therebetween and depressed against the surface of the abradable material, will result in a controlled removal of abradable material along a path traced by the tips of the fan blades.
In addition to the features mentioned above, other aspects of the present invention will be readily apparent from the following descriptions of the drawings and exemplary embodiments, wherein like reference numerals across the several views refer to identical or equivalent features, and wherein:
An intake portion of one exemplary embodiment of a turbofan jet engine 5 is depicted in
An abradable material lining 30 is visible along the inside of the fan housing 10, along the rotational travel path of the blade tips 25. During fan rotation, a minimized gap 35 separates the blade tips 25 from an adjacent (contact) surface 40 of the abradable material lining 30. In this particular example, an area of contact 45 between the blade tips 25 and the abradable material lining 30 is visible. It may be desirable to remove an amount of the abradable material lining 30 in this area 45 so as to minimize or eliminate further contact thereof by the blade tips 25 of the fan 15.
One exemplary embodiment of an abradable material removal tool 50 according to the invention is depicted in
As shown, the abradable material removal tool 50 includes an abradable material contacting base 55 having a leading end 55a, a trailing end 55b, and a curved profile C that corresponds to the curvature (i.e., circumference) of the abradable material contact surface 40 when the abradable material removal tool is in a proper working orientation (see
For reasons described in more detail below, the abradable material contacting base 55 is also of a size and shape that allows it to fit accurately between adjacent blades 20 of the jet engine fan 15 and to trace the path followed by the blade tips 25. More particularly, the abradable material contacting base 55 preferably includes a long edge 60, and a shorter opposite edge 65 having a leading bevel or taper 70.
A rigid or semi-rigid rib 75 may extend from a top surface 80 or other portion of the base 55. The rib 75 preferably, but not necessarily, extends substantially perpendicularly upward therefrom to facilitate handling and use of the tool 5 (i.e., to act as a handle). The rib 75 may also help to maintain the desired curvature C of the base 55 or, in embodiments where the base itself is not sufficiently rigid to do so, may actually establish and maintain the curvature of the base.
The rib (handle) 75 may be of virtually any height and shape. However, the bottom edge thereof is preferably shaped to conform to the curvature C of the base 55. The rib 75 may be secured to the base 55 by any technique known in the art, such techniques being at least somewhat dependent on the materials used to construct the base and rib. When the base 55 and rib 75 are comprised of plastic materials, attachment of the rib to the base may be accomplished by, for example, adhesive bonding, vibratory welding, etc. Alternatively, the base 55 and rib 75 may be a unitary structure formed by molding, casting, etc. The rib 75 may also include cutouts/holes and/or protrusions of various shape and size for purposes of improving the handling and use of the abradable material removal tool 5.
Use of the abradable material removal tool 5 to remove an amount of abradable material from within a turbofan housing also requires an abrasive material. To that end, this particular exemplary abradable material removal tool 5 is shown in
An abradable material removal tool of the invention is not limited to use with an abrasive material sheet, such as the sheet of sandpaper 95 shown in
As mentioned above, the base 55 of the abradable material removal tool 5 is dimensioned so as to fit between adjacent leading and trailing fan blades 20 of the fan 15. It is preferred that the base 55 be dimensioned such that the abradable material removal tool 5 may be easily inserted between adjacent fan blades 20, while also being properly oriented by the blades. The abradable material removal tool 5 is shown in such an orientation in
Referring still to
With the abradable material removal tool 5 positioned substantially as shown in
While certain embodiments of the present invention are described in detail above, the scope of the invention is not to be considered limited by such disclosure, and modifications are possible without departing from the spirit of the invention as evidenced by the following claims:
